The NFPA 11 Standard for Low-, Medium- and High-Expansion Foam, 2021 Edition, recommends discharge testing in order to confirm the concentration of the foam solution during the commissioning a new foam system (Section 12.6). This would mean that all systems need to be flow tested and foam discharged. However, due to the environmental concern with foam discharges, section 12.6.4 allows for “listed or approved” methods that do not require foam discharge.

Furthermore, NFPA 25 Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, 2023 Edition, recommends “an operational test of the foam proportioner shall be conducted annually” (Section 11.32). NFPA allows for “surrogate liquids” where approved by the AHJ (Section

Two methods that do not discharge foam and are used extensively in the industry are:

Surrogate Liquids Test Method – A surrogate liquid is a non-foaming, environmentally-acceptable liquid specially formulated to simulate the flow characteristics of the foam concentrate. There are a number of different surrogate liquid formulations to match the viscosity and flow characteristics of various foam concentrate products. For some new systems the surrogate liquid can be placed into the system foam tank, tested, and then rinsed prior to filling with foam concentrate. In many cases the foam tank is filled with foam so the surrogate liquid is placed in a portable bladder tank that is connected to the existing system using short fire hoses. In either case the system is discharged at the recommended flowrate and the proportioned stream is analyzed using on-line “real time” conductivity measurement instrumentation connected to a laptop data acquisition package. Similar to testing foam concentrate and water solutions, the surrogate liquid injection rate is determined by making a reference curve indicating conductivity versus % concentrate that is used by the data acquisition system.  When testing existing systems, additional connections and the portable surrogate liquid bladder tank are required to allow the surrogate liquid to be directed to the proportioner in place of the foam concentrate.

Water Equivalency Test Method - In this method, water is used as the surrogate liquid. Acceptance tests must first be conducted with the actual foam concentrate, discharging the system, and measuring the concentration using displacement, refractive index or conductivity. Once the foam concentrate meets the required concentration range, the foam concentrate is isolated from the system, and water is run through the proportioner in place of the concentrate at the same pressure and system water flowrate. The flowrate of the water being directed to the proportioner is recorded as the equivalency and this water flow rate is measured annually to ensure proper proportioning.

Both of these methods have been “certified” by an independent agency in the fire protection industry. These methods may be the AHJ’s preferred or required method for foam system acceptance and annual maintenance testing.

 Summary of Test Methods to Verify Foam Proportioning


Foam Concentrate

Surrogate Liquids

Water Equivalency

Method Used to Estimate Foam Solution Concentration

Time foam concentrate and water displacement


Measure the conductivity of the foam solution


Measure the refractive index of the foam solution

Measure the conductivity of the surrogate liquid/water Solution.


Measure the water flowrate entering the proportioner in place of the foam concentrate.

Foam Discharge During Acceptance Testing*




Foam Discharge During Annual Maintenance Testing*




(assuming the system was previously tested for foam/water equivalency)


No additional equipment is required.

No additional equipment is required for the acceptance test if the surrogate liquid is put into foam tank.


Additional tank and hose line are required for annual testing.

Additional tank and hose line are required for both the acceptance test and the annual testing.

*Proper disposal of foam solution, surrogate liquid, and/or water discharged from the system is required.


Here are vendors offering alternatives to foam discharge testing:

  • Vector Fire Technology, Inc.

If you have any questions regarding this article, please contact Dyne Fire Protection Labs at or (800) 632-2304.

©Dyne Fire Protection Labs 2023